The influence of flexural modulus effect on product design in injection molding

2021-03-23 12:53:08 admin

The influence of flexural modulus effect on product design in injection molding

In the physical properties of plastic materials, you will always see the flexural modulus (Flexural Modulus). Simply put, the flexural modulus is the strain generated by the bending stress than the upper bending, which indicates that the material resists bending deformation within the elastic limit Ability. The schematic diagram of the flexural modulus of PC is as follows:

In the measurement of flexural modulus, ASTM and ISO have slight differences in the size of test specimens and test methods, so the values from the two different standards are actually not good for direct comparison. The best method is to compare. Agree with the value under the method.

Speaking of this, some students may ask that the physical properties of plastic raw materials have not only flexural modulus but also tensile modulus. It depends on which modulus is better. My opinion is to first look at the specific application, that is, the state of the product in service, whether it is more bent or stretched. When it is difficult to determine the two, then I recommend looking at the tensile modulus first. This is because compared with the tensile modulus test method, the two splines are subject to different constraints, resulting in a slight difference in the accuracy of the mechanical model-stretching is two-stage clamping and stretching, and bending is two-stage support. Forced in the middle. Therefore, the force model of tensile modulus is relatively accurate. In addition, when the plastic spline is bent under a force during the test, a part of plastic deformation will occur, which causes the value read out to be actually too large:

So if you compare the flexural modulus and tensile modulus of some materials, there is roughly a multiple relationship of 1.4-1.5. Of course, not all plastic materials have this proportional relationship.

So what is the flexural modulus effect? To put it simply, when a material with a low modulus is subjected to the same force, the deformation will be greater than that of a material with a high modulus. In other words, on the same product, the difference between the deformation of a material with a low modulus and a thicker wall will be greater than that of a material with a higher modulus.

That is to say, D2/D1 will be greater than d2/d1. This difference will not make much difference to the performance of the product under the general condition of no force, but if it is under force, such as when falling, it will It will cause greater local deformation, resulting in sharp corners (Notch), and everyone knows that once sharp corners are generated, stress concentration will inevitably result in reduced local product strength, which may cause product failure.

In order to make it easier for everyone to understand, we can wirelessly thicken the parts of d1 and D1, so that the deformation of the two when subjected to force can be ignored, and we can only consider the deformation of d2 and D2. Obviously, the deformation of D2 will be greater than the deformation of d2, so there is a greater possibility of excessive deformation under force, and even formation of sharp corners (notch).